1. Field of the Invention
The present invention relates to an aqueous ink using a water-insoluble coloring material as a coloring material, and an ink jet recording method, an ink cartridge, a recording unit, an ink jet recording apparatus, and an image each using the aqueous ink.
2. Description of the Related Art
Coloring materials of inks for use in ink jet recording are mainly classified into dyes and pigments; the use of a dye as a coloring material has been conventionally a mainstream in order to obtain ease as an aqueous ink and high color developability of a formed image. In recent years, however, the development of an aqueous pigment ink using a pigment as a coloring material has been advanced for the purpose of, for example, additionally improving the weatherability of an image. The following procedure has been widely performed: a polymer dispersant (hereinafter referred to as “dispersant”) or the like is used in the pigment ink as a dispersant for the pigment which is insoluble to water.
An image formed of a pigment ink is excellent in weatherability as compared to an image formed of a dye ink, but the former image involves a problem in that the scratch resistance of the former image is lower than that of the latter image. A proposal concerning a contrivance on a water-soluble polymer to be incorporated into ink has been made to solve the problem (see Japanese Patent Application Laid-Open No. H08-269374).
However, scratch resistance requested of a conventional recorded article, the scratch resistance being at such a level that a coloring material is not scraped off when an image is scratched with a finger or the like, does not suffice for an image to be displayed outdoors such as a poster, a panel, a sign, or a point-of-purchase advertisement, so a high degree of scratch resistance is requested of such image. For example, a considerably large recording medium such as an A0-size medium or an A1-size medium is often used in applications where a poster or an advertisement is printed, so the recording medium on which an image has been formed is generally rolled into a cylindrical shape upon carrying of the medium. In addition, upon rolling of the recording medium, the image is scratched with a sharp portion such as a corner of the recording medium in some cases. In such cases, even when a conventional pigment ink credited with satisfying the scratch resistance of the image at a high level is used, a flaw is formed on the formed image, and a coloring material is scraped off. In the case of the conventional pigment ink, the problem occurs at a considerable frequency.
In addition, a problem similar to that described above occurs in other situations such as a situation in which an image formed of a pigment ink is lightly touched with a sharp product such as a nail upon sticking of the image as a poster outdoors. In this situation, as in the case of the foregoing, the following problem occurs at a considerable frequency: the coloring material of the image formed of the pigment ink is scraped off. As described above, particularly when a pigment ink is selected as an ink for use in a large ink jet recording apparatus, a scratch resistance higher than a conventional one is requested, the scratch resistance being at such a level that the coloring material of an image is not scraped off even when the image is touched with a sharp product such as a corner of a recording medium or a nail. The above-mentioned problem has been serious in a pigment ink in association with the expansion of the applications of an ink jet recorded image.
The scratch resistance of an image formed of a pigment ink has been heretofore of concern, so various methods have been proposed to achieve high scratch resistance. However, in most of the methods, investigation has been conducted on a small ink jet recording apparatus for use in offices and home applications, so the mere use of a conventional technique results in at most an image having such scratch resistance that no flaw is formed when a recording medium is touched with a finger. In other words, it has been still unable to solve a problem concerning the scratch resistance of an image formed of a pigment ink in such case as the image is touched with a sharp product such as a corner of a recording medium or a nail.
To solve such problem, in order that the scratch resistance of an image formed of a pigment ink may be improved, the following idea has been made: a large amount of a polymer such as a dispersant is incorporated into the ink in order that a pigment constituting the image may be additionally strongly fixed to a recording medium. However, the addition of an excessive amount of a polymer or the like to the ink may involve the emergence of other problems such as a reduction in dispersion stability of the pigment or the like in the ink; a reduction in storage stability of the ink; and a reduction in ejection stability of the ink.